Display screen or portion thereof with graphical user interface for a boiler or water heater



FIG. 1 is a front view of a display screen or portion thereof with graphical user interface for a boiler or water heater showing our new design; and,

FIG. 2 is a front view of a second embodiment of a display screen or portion thereof with graphical user interface for a boiler or water heater showing our new design.

The outer perimeter shown in broken line in the FIGURES depicts a display screen or portion thereof and forms no part of the claimed design. The broken line text forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with graphical user interface for a boiler or water heater, as shown and described. 